Semi-submerged marine platform structure

ABSTRACT

A semi-submerged platform structure to be used for workings at sea, comprising a pair of relatively short central lower hulls arranged in alignment with and spaced apart from each other, a pair of relatively long side lower hulls arranged each on each side of the row of said central lower hulls in parallel and in symmetrical relation with respect thereto, six upright columns respectively provided on said central and side lower hulls such that said columns occupy the vertices of a regular hexagonal shape respectively, a working platform supported by said columns and structural members interconnecting said lower hulls, columns and working platform.

United StatesPatent 191 Arita et al.

[ Aug. 20, 1974 SEMl-SUBMERGED MARINE PLATFORM STRUCTURE [75] I Inventors: Yukio Arita; Katsuya Ninomiya, both of Hiroshima; Eiichi Miwa, ltsukaichi, all of Japan [73] Assignee: Mitsubushi Jukogyo Kabushiki Kaisha, Tokyo, Japan 22 Filed: June 6,1973

21 Appl. No.: 367,407

[30] Foreign Application Priority Data June 26, 1972 Japan 47-63191 [52] US. Cl. 1l4/0.5 D, 114/435 [51] Int. Cl B63b 35/00, B63b 35/44 [58] Field of Search 114/05 D, 43.5; 61/465 [56] References Cited UNITED STATES PATENTS 3,154,039 10/1964 Knapp ll4/0.5 D 3,271,964 9/1966 Wolff 114/05 D X l/l97l 4/1972 Bonnafous ll4/0.5 D 3,653,349 Brown ll4/O.5 D

Primary Examiner-Trygve M. Blix Attorney, Agent, or FirmCushman, Darby and Cushman [5 7 ABSTRACT A semi-submerged platform structure to be used for workings at sea, comprising a pair of relatively short central lower hulls arranged in alignment with and spaced apart from each other, a pair of relatively long side lower hulls arranged each on each side of the row of said central lower hulls in parallel and in symmetrical relation with respect thereto, six upright columns respectively provided on said central and side lower hulls such that said columns occupy the vertices of a regular hexagonal shape respectively, a working platform supported by said columns and structural members interconnecting said lower hulls, columns and working platform.

1 Claim, 6 Drawing Figures SEMI-SUBMERGED MARINE PLATFORM STRUCTURE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a semi-submerged platform structure to be used for workings at sea, and more particularly to such a semi-submerged platform structure which has improved stability gainst capsize upon casual failure of the structural members caused by collision against floating obstacles such as ice drifts or other reasons, while maintaining its excellent manoeuvability and transport characteristic at sea.

2. Description of the Prior Art Conventional semi-submerged platform structures to be used for workings at sea have had limited use only in the regions of sea free of ice drifts and, under the circumstances, there have been developed platform structures of types having excellent manoeuvability and transport characteristic in waves but these platform structures are not entirely satisfactory in respect of safety against shocks given by ice drifts or other floating obstacles.

For instance, there has been proposed a three-leg semi-submerged platform structure which, as shown in FIGS. 1 and 2, comprises three footings a as the main buoyant members, columns b mounted on said footings a respectively for securing the stability of the platform structure, a working platform supported by said columns b and bracings d interconnecting said columns b. This prior art platform structure is defective in that, when the joints e of the bracings d and columns b have once been broken by the shocks given by ice drifts or other floating obstacles, the platform structure can not longer maintain its stability and overturns.

There has also been proposed a multi-leg platform structure comprising at least four footings a and four columns b. This type of platform structure has no danger of capsize because, even when one leg fails, the structure can maintain its stability with the other three or more legs, but on the other hand, has the disadvantage that the resistance to the structure during towing becomes extremely large, degrading the transport characteristic of the structure.

A two-lower hull type semi-submerged platform structure which has been developed in the past'and is shown in FIGS. 3 and 4 comprises a pair of parallel lower hulls f, f, a group of upright columns g provided on each lower hull f, a working platform h supported by said columns g and bracings i interconnecting said columns g and working platform h. This prior art platform structure is advantageous in that the two rope resistance is small and therefore, the structure has excellent transport characteristic, but is unsatisfactory in that it is poor in balancing characteristic and especially the structure involves the danger of capsize when cracks occurring in one of the lower hulls grow and the bilged compartments of said hull increases.

SUMMARY OF THE INVENTION The present invention consists in a semi-submerged platform structure to be used for workings at sea, which is free of such disadvantages of the prior art structures as described above and which comprises a pair of relatively short central lower hulls arranged in alignment with and spaced from each other, a pair of relatively long side lower hulls arranged on both sides of said.

aligned central lower hulls in parallel and in symmetrical relation thereto, six upright columns respectively mounted on said central and side lower hulls such that they occupy the vertices of a regular hexagonal shape, a working platform supported by said columns and bracings interconnecting said lower hulls, columns and working platform. The object of the present invention is to provide an improved semi-submerged platform structure to be used for workings at sea which has improved stability against capsize upon casual failure of the structural members caused by collision against floating obstacles such as ice drifts or other reasons, while maintaining its excellent manoeuvability and transport characteristic at sea.

In the semi-submerged marine platform structure according to the present invention, the working platform is supported by six columns, so that even when one of the six columns is broken by the shocks given thereto by floating obstacles such as ice drifts, the structure is capable of maintaining its stability with the remaining five columns and does not overturn.

Further, the marine platform structure of the present invention comprises four lower hulls on which the columns are respectively mounted, and of these lower hulls, the two relatively short central lower hulls are arranged on a straight line passing the center of the platform structure in spaced relation and the remaining two relatively long side lower hulls arearranged on both sides of said aligned central lower hulls in parallel and in symmetrical relation thereto. Furthermore, the six columns extending upright from the lower hulls respectively are arranged such that they occupy the vertices of a regular hexagonal shape. Therefore, the platform structure is symmetrical with respect to the center thereof and well resistive to external forces applied thereto in any direction. Such arrangement of the structural members of the platform structure, plus the effects of the six columns, renders the structure highly safe against shocks given by floating obstacles and sufficiently usable even in the regions of sea jammed with ice drifts.

It should also be noted that the platform structure of the present invention has excellent manoeuvability and towing characteristic in the waves as the four lower hulls are arranged substantially in three rows, the two outer rows of lower hulls being arranged symmetrically with respect to one central row of lower hulls.

As may be understood from the foregoing description, the semisubmerged marine platform structure of the invention is designed so as to ensure the safety thereof against destruction caused by collision with floatingobstacles such as ice drifts, without impairing the manoeuvability and transport characteristic which are the basic features of this type of marine platform structure, and is adapted for use as a platform structure for undersea oil-well drilling, marine public works or marine plants.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 respectively are a plan view and a side view of a prior art three-leg semi-submerged marine platform structure;

FIGS. 3 and 4 respectively are a plan view and a side view of a prior art two-lower hull type semi-submerged marine platform structure;

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention will be described hereunder with reference to the embodiment thereof shown in the drawings.

The platform structure of the invention includes a pair of relatively short central lower hulls 1a and a pair of relatively long side lower hulls 1b. The relatively short central lower hulls 1a, 1a are arranged with their longitudinal axes lying on a straight line passing the center of the platform structure and are spaced from each other, while the relatively long side lower hulls lb, 1b are arranged on each side of the row of said central lower hulls la, la in symmetrical relation with respect thereto, with their longitudinal axes extending parallel to said straight line. Thus, the four lower hulls are arranged in three rows substantially parallel to each other, so as to enhance the transport or towing characteristic of the platform structure. The opposite ends of each of the lower hulls are shaped in a semicircular shape as viewed from the upper side, so as to minimize the tow rope resistance and thereby enhancing the towing characteristic of the platform structure.

The relatively short central lower hulls la, 1a are made in a size large enough to provide a buoyancy sufficient to support the total weight of the platform structure during towing of said structure. Six columns 2 respectively are extended upwardly from the outer ends of the central lower hulls 1a, 1a and the opposite ends of each of the side lower hulls 1b, lb, the arrangement of said columns 2 being such that each column is positioned at each vertex of a regular hexagonal shape. A working platform 3 is mounted on the top ends of the columns 2 to be supported thereby. Each of the columns 2 is of a size necessary to secure the stability of the platform structure and is so designed as to minimize the sway of the platform structure in the waves.

The lower hulls 1a, lb and the working platform 3 are interconnected by vertical members 4, and columns 2 are suitably interconnected by horizontal bracings 5, and furthr, the columns 2 and the vertical members 4, and the vertical members, are suitably interconnected by horizontal bracings 6. Beneath the central portion of the working platform 3 is left open to provide a working space 7, and the vertical members 4 and horizontal bracings 5, 6 serve as structural members to increase the strength and rigidity of the platform structure.

The interiors of the lower hulls la, 1b and the columns 2 are respectively divided into water-tight compartments by sealing partition walls 8, 9, and these compartments are used as storage tanks for ballast, fresh water and fuel oil. The sizes of the respective compartments are suitably selected in consideration of the degree of inclination of the platform structure in the event when water intrudes into the compartments.

The marine platform structure of the present invention may be provided in either a self-propelled type or non-self-propelled type. When the platform structure is of the self-propelled type, propeller means 11 are disposed projectably in recessed portions 10 respectively formed in the lower side of the hulls la, lb. The propeller means 11 when not in use are retracted into the recessed portions 10 and completely concealed therein.

The marine platform structure of the construction described and illustrated herein travels on the sea by its own propelling force or by being towed by a towboat, while being held afloat on the sea by the buoyancy of the lower hulls la, lb which are then at a light draft level B shown in FIG. 6, and reaches the area where it is intended to be used. In the area of working, the platform structure is anchored to the sea-bottom and lowered into the sea by lowering the lower hulls to the level A shown in FIG. 6 by introducing sea water into the ballast tanks. Then, the desired work is performed using the platform structure as a foothold which is held afloat with the columns 2 being in a semi-submerged state. The platform structure may be set directly on the sea bottom where the sea is shallow in depth.

When it is desired to raise the platform structure upon completion of the work by the buoyancy of the lower hulls la, 1b, this can be achieved by discharging the water from the ballast tanks by means of pumps.

Although the present invention has been described and illustrated herein in terms of a specific embodiment thereof, it should be understood that the present invention is not restricted only to the embodiment but many changes and modifications are possible within the scope not deviating from the spirit of the present invention.

What is claimed is:

1. A semi-submerged platform structure to be used for workings at sea, comprising a pair of relatively short central lower hulls arranged in alignment with and spaced apart from each other in a row, a pair of relatively long side lower hulls arranged each on each side of the row of said central lower hulls in parallel and in symmetrical relation with respect thereto, six upright columns respectively provided on said central and side lower hulls such that said columns occupy the vertices of a regular hexagonal shape respectively, a working platform supported by said columns and structural members interconnecting said lower hulls, columns and working platform. 

1. A semi-submerged platform structure to be used for workings at sea, comprising a pair of relatively short central lower hulls arranged in alignment with and spaced apart from each other in a row, a pair of relatively long side lower hulls arranged each on each side of the row of said central lower hulls in parallel and in symmetrical relation with respect thereto, six upright columns respectively provided on said central and side lower hulls such that said columns occupy the vertices of a regular hexagonal shape respectively, a working platform supported by said columns and structural members interconnecting said lower hulls, columns and working platform. 